สอบถามหน่อยครับ มันเออเร่อ Warning: Invalid argument supplied for foreach() นะครับ

 <script src="http://code.jquery.com/jquery-1.8.3.js"></script>
        <link rel="stylesheet" href="http://code.jquery.com/ui/1.10.0/themes/base/jquery-ui.css" />
        <script src="http://code.jquery.com/ui/1.10.0/jquery-ui.js"></script>
<?
  $sql6="select * from tb_detailbookinga where id_rooma='$id_rooma'";
			  $result6=mysql_query($sql6);
			  while ($read_data6=mysql_fetch_array($result6)){
				 $check_ina=$read_data6[check_ina];
				  $check_outa=$read_data6[check_outa];
$arr[] = $check_ina;
$arr[] = $check_outa;
}
   foreach ($arr as $value) 
{
	$format[] = date("j-n-Y",strtotime($value));
}

?>
        <script>
            var unavailableDates = <? echo json_encode($format); ?>;
            function unavailable(date) {
                dmy = date.getDate() + "-" + (date.getMonth()+1) + "-" + date.getFullYear();
                if ($.inArray(dmy, unavailableDates) <0) {
                    return [true,"","สามารถจองได้"];
                } else {
                    return [false,"","ไม่สามารถจองได้"];
                }
            }
            $(document).ready(function(){
                $('#datepicker').datepicker({ beforeShowDay: unavailable });
				 $('#datepicker1').datepicker({ beforeShowDay: unavailable });
            });
        </script>